Recently, airbag systems for vehicle safety device are increasingly installed in automobiles. The increasing demand for vehicle safety accelerates the installment of new types of airbags in automobiles, such as side airbags and side curtain airbags which protect passengers from the impact by side crash, in addition to conventional driver and front passenger airbags.
The side airbags and side curtain airbags are required to be highly airtight, because they must retain their form for several to about 10 seconds after their deployment in order to hold passengers at the event of side crash or overturn of automobiles. Thus coated airbags made of silicone-resin-coated fabric are employed for their improved airtightness.
Base fabrics for airbags are woven with synthetic yarns, and the finishes on the yarns are removed from the fabrics in scouring process. Fabrics woven with water-jet looms are not subsequently scoured because water jet in weaving process removes the finishes.
For manufacturing coated airbags, finishes remaining in base fabrics may cause insufficient adhesion between the base fabrics and silicone resins leading to insufficient airtightness of resultant airbags. Thus finishes remaining in base fabrics must be completely removed for manufacturing quality airbags. On the other hand, the demand for space-saving compact airbags is increasing for saving fuel consumption of automobiles.
For meeting the demand of compact airbags, low-density base fabrics must be woven with low-fineness yarns, and the strength of the low-density base fabrics is maintained by increasing the tenacity of the low-fineness yarns.
The tenacity of the yarns can be increased by increasing the draw ratio and the temperature of draw rolls in spinning synthetic filament for the yarns. The increased draw roll temperature may cause the troubles due to stain on draw rolls, such as broken filament and ends down, which were not identified as the troubles in the conventional spinning processes.
PTL 1 discloses a spin finish for filament yarns to be processed into base fabrics for quality silicone-coated airbags. The finish contains 50 to 70% of monohydric fatty acid ester with M.W. of 500 to 700, 15 to 35% of EO/PO polyether with M.W. of 1000 to 2000, 0.1 to 3.0% of a hindered phenol antioxidant, 0.1 to 2.0% of an organic phosphate ester, 0.5 to 2.0% of an organic sulfur compound and 0.1 to 1.0% of a silicone compound. The finish in the PTL 1, however, generates much fume on high-temperature rolls required recently in spinning process, and causes troubles including poor working environment and broken filament due to poor heat resistance of the finish.
PTL 2 discloses a spin finish containing 30 to 50% of the ester derived from a dibasic acid and a monohydric alcohol, 20 to 50% of the ester derived from a monobasic acid and a compound having at least three hydroxyl groups per molecule, 1 to 10% of the ester polymer with M.W. of 10000 to 30000 derived from a dibasic acid and a compound having at least three hydroxyl groups per molecule, and 0.5 to 5% of alkyl phosphate amine salt with M.W. of 1000 to 2000 for producing polyamide fiber useful for manufacturing airbags. The spin finish containing the ester polymer of high M.W. described in PTL 2, however, could not be removed sufficiently from the fabric of the yarn applied with the finish in scouring or in weaving with water-jet looms, and the fabric could not be well adhered with silicone resins.
PTL 3 discloses a finish composition for producing a thermoplastic synthetic fiber, which contains the diester of thiodipropionic acid and C12-C18 monohydric alcohol and POE (10 to 45) castor oil or hydrogenated castor oil in a weight ratio from 4:1 to 2:3. The airbag fabric made of the synthetic fiber applied with the finish resulted in insufficient adhesion of the fabric and silicone resins due to high amount of the total sulfuric acid in the finish.